The long term goal of our research is to characterize mechanisms that endow an organism with its ability to generate behavior that is plastic in the sense that it can be continuously modified to accommodate changes in the external environment. Our experiments are conducted in a relatively simple model system with experimentally advantageous features. In this system biting is generated when higher order command/modulatory neurons are activated. Bites are converted into bite-swallows when food contacts an animal and activates sensory neurons. Some of the food-induced alterations in feeding are coincident with activity in sensory neurons while other alterations occur after sensory neurons are no longer active, i.e., they rely on a ?memory? of the stimulus. In the previous grant period my laboratory identified sensory neurons activated by food that initiate bite to bite-swallow transformations. Work described in this application follows up on an exciting recent finding concerning how afferent-induced changes in feeding are likely to occur. Namely, our data suggest that afferent input only modifies motor activity if it is ?gated-in?. If afferents are activated in quiescent animals, reflex or motor output will not be generated. In contrast, when afferents are activated while behavior is ongoing, feeding movements can be altered. Afferent input is, however, only gated-in at certain times. This arrangement permits afferent-induced modifications of behavior but does not permit afferent-induced reconfigurations of behavior. Experiments described in this proposal will determine how this regulation of afferent transmission occurs. We will test a specific hypothesis that postulates that gating occurs at least in part by the selective control of spike propagation in sensory neurons. We will characterize cellular mechanisms that are utilized and we will conduct experiments in semi-intact preparations that will relate cellular findings to behavior. We believe that our work will provide insights into dysfunctions of the nervous system that are associated with attention deficits. Data indicate that at least in some cases (e.g., in schizophrenia) these dysfunctions are specifically associated with defects in sensory gating.